Chromatic dispersion (CD) in optical fibers or other optical components is a widespread physical phenomenon that generally occurs during the transmission of optical signals in dispersive media.
In highly developed optical transmission systems, chromatic dispersion becomes relevant as an interfering effect, for example, at high transmission rates or great optical transparency lengths. To reduce the chromatic dispersion, which is accumulated along an optically transparent transmission path, it is known to insert dispersion-compensating elements into the transmission paths. Among other things, dispersion-compensating fibers (DCFs) or chirped fiber gratings are used for that purpose.
Problematical, however, in the compensation of chromatic dispersion is that in general, it has no constant value for a given transmission length, but rather is subject to changes over time. In addition to being triggered by other environmental influences, such changes are also triggered by, inter alia, temperature fluctuations, since the chromatic dispersion of optical components such as glass fibers is temperature-dependent.
These changes in the chromatic dispersion are relatively small, so that the change in signal quality caused by them is generally negligible in transmission systems currently installed.
In the case of newer, highly developed transmission systems, for instance, those with data transmission rates above 10 GBit/s or very long transmission paths, however, these changes already have a very disruptive effect on the optical signal quality. For such transmission systems, methods for automatic or adaptive dispersion compensation (ADC) are therefore considered to be absolutely necessary.
Some ADC implementation techniques are already known. A device for ADC proposed by K. Yamane in “New functionalities for advanced optical interfaces (dispersion compensation)”, workshop on IP/optical in Chitose, Japan, Jul. 9-11, 2002 is based on an optical circulator in conjunction with a complex free-beam optical system having six partially mechanically adjustable optical components. However, this design approach is very costly. In addition, its long-term stability is doubtful.